Pneumatic tires for high speed applications experience a high degree of flexure in the crown area of the tire as the tire enters and leaves the contact patch. This problem is particularly exacerbated on aircraft tires wherein the tires can reach speed of over 200 mph at takeoff and landing.
When a tire spins at very high speeds the crown area tends to grow in dimension due to the high angular accelerations and velocity tending to pull the tread area radially outwardly. Counteracting these forces is the load of the vehicle which is only supported in the small area of the tire known as the contact patch.
In U.S. Pat. No. 5,427,167, Jun Watanabe of Bridgestone Corporation suggested that the use of a large number of belt plies piled on top of one another was prone to cracks inside the belt layers which tended to grow outwardly causing a cut peel off and scattering of the belt and the tread during running. Therefore, such a belt ply is not used for airplanes. Watanabe found that zigzag belt layers could be piled onto the radially inner belt layers if the cord angles progressively increased from the inner belt layers toward the outer belt layers. In other words the radially inner belt plies contained cords extending substantially in a zigzag path at a cord angle A of 5 degrees to 15 degrees in the circumferential direction with respect to the equatorial plane while being bent at both sides or lateral edges of the ply. Each of the outer belt plies contains cords having a cord angle B larger than the cord angle A of the radially inner belt plies.
In one embodiment each of the side end portions between adjoining two inner belt plies is provided with a further extra laminated portion of the strip continuously extending in the circumferential direction and if the radially inner belt plies have four or more in number then these extra laminated portions are piled one upon another in the radial direction. The inventor Watanabe noted the circumferential rigidity in the vicinity of the side end of each ply or the tread end can be locally increased so that the radial growth in the vicinity of the tread end portion during running at high speed can be reduced.